Hydrotreating catalyst

ABSTRACT

Highly active catalysts of molybdenum and Group VIII metals are prepared by impregnating a support with highly stable solutions of the active metal compounds and an acid of phosphorus having a P/MoO3 weight ratio of 0.1-0.25 and an initial pH of 1 to about 2.

United States Patent 1191 Mickeison Aug. 28, 1973 [54] HYDROTREATINGCATALYST 3,232,887 2/1966 Pessimisis 252/435 3,442,794 5/1969 Van Heldenet a1 208/1 1 1 [75] M'ckelsm" Yrba 3,459,678 8/1969 Hagemeyer, Jr. eta1 252/435 Callf- 3,474,041 10/1969 Kerr 252/435 x 3,629,146 12/1971Adams 252/435 [73] Ass'gnee' ggfx g'g i g 3,684,695 8/1972 Neel et a1.208/110 [22] Filed: Apr. 1, 1971 e 21 A N I Primary Examiner-C. F. Dees1 PP o Attorney-Milton W. Lee, Richard C. Hartman and Related U-S.Application Data Lannas Henderson [63] Continuation-impart of Ser. No.837,340, June 27, 1969, abandoned, which is a continuation-in-part ofSer. No. 761,322, Sept. 20, 1968, abandoned.

[52] US. Cl 252/435, 252/437, 252/455 R, [57] ABSTRACT 252/458, 252/45951 1111. c1 B01 j 11/82 g y active catalysis of molybdenum and Group[58] Field of Search 252/435, 455 R, 458, metals are P p y p g g a uppth 252/459 highly stable solutions of the active metal compounds and anacid of phosphorus having a P/MoO weight [56] R f e Cit d ratio of0.1-0.25 and an initial pH of l to about 2.

7 UNITED STATES PATENTS 3,287,280 11/1966 Colgan et al 252/435 20Claims, N0 Drawings 1 HYDROTREATING CATALYST BACKGROUND AND DESCRIPTIONThis application is a Continuation-lnPart of my copending application,Ser. No. 837,340, filed June 27, 1969 which in turn was aContinuation-ln-Part of application Ser. No. 761,322, filed Sept. 20,1968, both of which are now abandoned.

Hydrotreating catalysts comprising a Group Vlll metal, particularlycobalt, or nickel, a Group Vl metal, particularly molybdenum ortungsten, or their oxides or sulfides, and phosphorus on an alumina orsilicastabilized alumina'base have been disclosed in U. S. Pat. Nos.3,232,887 and 3,287,280. Such catalysts are extensively employed fordenitrogenation or desulfurization of petroleum feed stocks as wellasfor other hydrogenation reactions. U. S. Pat. No. 3,287,280, inparticular, describes methods and impregnating solutions for preparingsuch catalysts consisting of molybdenum and nickel salts stabilized withphosphoric acid in an aqueous medium. This patent discloses thedesirability of maintaining the amount and ratio of the constituents ofthe impregnating solution. within relatively narrow ranges.

It has now been found that the ratio of phosphorusto-Group VI metal,particularly molybdenum, employed in such solutions is critical, andthat the activity of the resulting catalysts is substantially enhancedby the use of a higher phosphorus-to-molybdenum metal ratio than thatemployed in the conventional catalyst preparations. In addition, it hasbeen found that proper regulation of the pH of the solution is essentialin order to obtain maximum catalytic activity.

For catalysis of denitrogenation or desulfurization reactions, thecatalytic metals are generally employed in the form of oxides inassociation with a carrier material. Conventionally, the catalyticmetals are applied to the carrier by impregnation with a solution of acompound of the metal, followed by calcination to convert the catalyticmetal compounds to oxides. The use of an acid, such as phosphoric acid,as a component of the impregnating solution is disclosed in theabovementioned U. S. patents. The disclosed function of the acid is thestabilization of the impregnating solution containing both the Group VIand the Group Vlll metal compound.

However, I have found that stabilization of the impregnating solutionper se affords a solution for only one of the major problems associatedwith the impregnation of catalyst with Group VIII and Group VI metalcomponents. It is generally recognized that the formation of an evenlydistributed layer of the active compo-' nents such as the metals,oxides, or sulfides throughout the entire surface area of the catalystsupport enables the most efficient utilization of the entire catalystsurface area, i.e., contact surface, and thereby provides the mostactive catalyst in most applications. The impregnation of such catalystssupports with the active components herein discussed by the use ofunstabilized" solutions is subject to several distinct disadvantages.For example, precipitation of the active components from solution evenprior to contact with the catalyst support occurs to such a significantextent that a considerable amount of the active components are lost aswaste material. The catalysts thus formed do not comprise an evenlydistributed active component layer. In addition, the active componentsare deposited on the support surface as crystalline aggregates resultingin a heterogeneous non-uniform catalytic surface of inferior activity.Precipitation of the active components from the impregnating solutionbecomes particularly acute at higher concentrations. For this and otherrea-' sons hereinafter discussed, it has previously been necessary toemploy impregnating solutions of such reduced concentration thatmultiple impregnations were necessary to deposit the desired amount ofactive material on the support surface. The multi-step impregnationprocedure necessitated by solution instability generally involves therepeated cyclic contact of a support such as silica or alumina with animpregnating solution of relatively low concentration. Intermittentpartial drying between impregnation cycles is often necessary to renderthe deposited materials in the form less susceptible to extraction onsubsequent contact with'additional impregnating medium. This procedureinvolves a rather involved cyclic batch operation and is much lessattractive than a simpler single step or continuousimpregnation-calcination procedure. However, the use of that simplifiedprocedure is not advisable due to the instabilityof the impregnatingsolutions. The catalyst thus produced are of inferior activity. Thisresult is believed to be attributable to the distribution of activecomponents on the surface of the support medium in a non-uniform manneras relatively large crystalline aggregates.

The same disadvantages are associated with the use of the so calledstabilized impregnating solutions heretofore employed. The stability ofthose solutions is not sufficient to enable the use of impregnatingmedia of sufficient concentration to deposit the desired amount ofactive components on a catalyst support in a single step. An evendistribution cannot be achieved in a single step due to the fact thatimpregnating solutions of sufficiently high concentration cannot bemaintained in a stable form.

I have also observed that even the catalysts produced by multi-stepimpregnation with the dilute stabilized solutions of the prior art aremarkedly inferior to those obtainable by the procedures hereindescribed. The stabilized solutions of the prior art, such as thosediscussed in U. S. Pat. Nos. 3,232,887 and 3,287,280 are more stable inthe classical sense than are solutions containing no stabilizingcomponent. Precipitation from these stabilized solutions is less likelyin the ab sence of a support surface, provided the concentration ofactive components in the impregnating solution is relatively low.However, the active components deposit from these solutions on thesupport surface as crystallites. This form of deposition is apparentlydue to the promotion of crystallization on the active components by thesupport surface. Whatever the cause of crystallite formation, it isunderstandable that once crystallites-form they tend to promotecontinued crystallization. The result is isolated crystal growth andcrystalline aggregate formation in the pores and on the surface. Theobvious consequence of this sequence of events is the formation of anunevenly distributed layer of active components on the surface of thesupport matrix. Such heterogeneity of the catalyst surface is believedto be accountable for the lower activity observed.

The problems observed in the impregnation step are not the only factorsinvolved in forming an active catalyst. The formation of a homogeneouscatalyst surface alone does not solve all the problems involved in thepreparation of these catalysts. On the contrary, I have observed thatthe manner in which the catalyst is treated subsequent to impregnationhas a dramatic influence on the activity of the finished product. It haspreviously been considered most expeditious to expose the impregnatedsupport to a preheated furnace in which volatile materials, e.g., water,are rapidly expelled. However, I have discovered that drying of theimpregnated support should be conducted at a rate much less than themaximum in order to obtain the most active product. Although the reasonsfor this result are not known with certainty, it is presumed that eitherrapid crystallization or steaming of that catalyst are at leastpartially accountable. It may be that accelerated drying and thecorresponding rapid increase in the solution concentration on thesurface promote the formation of crystallites and crystallineaggregates.

It is therefore one object of this invention to provide a catalyst ofincreased activity. It is another object of this invention to provide ahighly active catalyst composite of refractory oxides, Group VIII andGroup VI metals, oxides and/or sulfides. It is another object of thisinvention to provide an improved catalyst preparation method. It isanother object of this invention to provide an improved method forimpregnating refractory oxide supports with catalytically activematerials. It is another object of this invention to provide catalystimpregnating solutions of improved stability. It is another object ofthis invention to provide a catalyst impregnation procedure whichenables the formation of evenly distributed catalytically active contactareas by a single step impregnation procedure. It is another object ofthis invention to provide an improved method for drying impregnatedcatalyst composites. Yet another object of this invention is theprovision of an impregnated catalyst drying procedure which enables theformation of homogeneous catalytically active component contactsurfaces.

DETAILED DESCRIPTION According to the present invention, it has beenfound that the use of amounts of phosphoric acid, particularly relativeto that of Group VI metal, greater than those taught by the prior art isnot only effective in stabilizing the impregnating solution but alsosubstantially enhances the catalytic activity of the finished catalyst.The reason for the enhanced activity of the catalysts of the inventionis not known with certainty but is believed to relate to the fact thatduring the preparation of the catalysts of the invention an amorphouscolloidal film of the impregnating materials is deposited on the surfaceof the support, whereas, in the prior art methods the impregnatingmaterials are deposited in crystalline form. This is believed to resultin more uniform distribution of the molybdenum and nickel ions on thesurface of the carrier throughout its pore structure when the process ofthe invention is employed. It can, in fact, be shown that solutionsprepared according to the process of the invention do not crystallizeorprecipitate upon standing for months at room temperature. Moreover, nocrystallized or precipitated material is formed upon drying thesolutions in an evaporating dish or in a thin film on glass, metal orceramic surfaces; instead, a transparent colloidal film is formed.Solutions outside the limits of concentration and pH of the inventioncrystallize or precipitate before or during drying and yield opaquefilms on surfaces. The effectiveness of these is demonstrated by theillustrative examples.

As previously mentioned, the conditions necessary to produce anamorphous as opposed to crystalline deposit, at the relatively highconcentrations necessary to produce a catalyst of the desiredcomposition in a single step are quite critical. It is presently feltthat the most critical of these process conditions are the pH of thesolution and the P/MoO, weight ratio. The pH necessary to achieve thisresult in the systems herein described must be within the range of] toabout 2 for the solution initially contacted with the substrate. I haveobserved that some increase in pH values slightly above 2, i.e., up toabout 2.5, can be tolerated during the latter stages of impregnationwhen the concentration of active components is substantially diminisheddue to the deposition of those components on the catalyst support.However, the pH should be maintained as close as possible to about 1.5,i.e., from 1.2 to about l.8. Deviations from that midpoint in eitherdirection render the impregnating solution less stable. The greater thedeviation, the greater the prospect of crystalline deposite formationand crystallite aggregation on the support surface.

In accordance with another embodiment of this invention a catalystcomprising a composite of a Group VIII and Group VI metal on arefractory oxide support of increased activity is prepared by drying animpregnated support under relatively mild conditions prior tocalcination. It is presently preferred that the impreg nated catalyst beheated gradually to a temperature only slightly in excess of thetemperature necessary to expel the impregnating solution'solventretained on the catalyst. As this solvent is generally water, it ispresently preferred that the drying temperature be allowed to graduallyapproach a temperature of at least about 220F, preferably from 220F toabout 250F. It is presently preferred that the heat up rate not exceedabout 20 F/minute. This temperature is then maintained for a periodsufiicient to expel substantially all of the solvent from the substrate.It is generally desirable to reduce the physisorbed water content bythis procedure to less than about 4 wt. percent and preferably less thanabout 2 wt. percent based on total catalyst weight. This generallyrequires drying periods of about 10 minutes to about 10 hours, dependingon the temperature employed, the rate at which air is passed over thecomposite, the depth of the composite layer and the particle size.Shorter drying periods can, of course, be tolerated at the highertemperatures. A corollary advantage, in addition to the prevention ofcrystallite formation, is accomplished by this procedure in thatsteaming and consequent decrepitation of the catalyst particles areavoided. These deleterious effects appear to result from rapid heatingto a point substantially above the boiling point of the solvent whichresults in the formation of substantial amounts of steam within theinterior pore volume of the catalyst support. Although the prevention ofthis latter efi'ect is believed to be less critical than the preventionof crystallite formation, it is desirable and is a corollary benefit ofthe preferred drying procedure.

It should be observed that the drying procedure referred to is not anecessary antecedent of the described impregnation procedure. Althoughrapid drying is believed to favor the formation of. crystallites, theextent of aggregate formation on drying is not nearly so great as tocompletely dissipate the advantage of the homogeneous active componentdispersion accomplished during the described impregnation procedure.Similarly the beneficial results ascribed to the preferred dryingprocedure are not limited to supports prepared by the impregnationprocedure detailed herein. However, the advantage of this approach ismore apparent when the impregnated support is relatively free ofcrystalline deposits prior to drying. The observance of rigid controlsduring the drying step would obviously be of little benefit with regardto crystallite formation in systems wherein a substantial proportion ofthe active components are already present in the form of crystallineaggregates due to the manner of impregnation. However, severaladvantages, such as the prevention of particle decrepitation, arerealized regardless of the physical form of the active metal deposit.

The required amount of phosphorus is most conveniently expressed as theratio of the weight of elemental phosphorus to the weight of the GroupVI metal oxide. For example, in the specific examples below, the amountof phosphorus is expressed in terms of the phosphorus-to-molybdenumoxide weight ratio, i.e., PlMoO It has now been found that this ratioshould be at least about 0.1 in order to achieve the desired improvementin the catalytic activity. On the other hand, the use of too high aconcentration of phosphorus generally results in diminished catalyticactivity. Consequently the P/MoO ratio in the product should be withinthe range of 0.1 to about 0.25, preferably from 0.12 to about 0.23.

Catalysts having these compositions are conveniently prepared by singlestep pore saturation techniques with solutions having P/MoO ratioscorresponding to those desired in the calcined product. The solutionsgenerally contain from l to 30, usually about 17 to about 30 wt.% M00about I to about 10, preferably I to 8 wt. percent of the selected GroupVIII metal oxide and I to about 6 wt. percent phosphorus on anequivalent basis. However, when the preferred single step poresaturation method is employed the solution preferably contains theequivalent of 17 to about 24 wt.% M00 1 to about 5 wt. percent of theGroup VIII metal oxide and 2 to about 6 wt. percent phosphorus.

When impregnation is accomplished by prolonged immersion of theforaminous base with excess solution, somewhat lower active componentconcentrations can be employed. For example, the equivalent oxide moleratios can be within the range of 10 to 17 wt.% M00 2 to l0,preferably 2to 4-wt. percent of the Group VIII metal oxide and l to 2 wt. percentequivalent elemental phosphorus. In these systems the P/MoO, ratio ispreferably somewhat lower than in the pore saturation techniques sincephosphorus is deposited at a faster rate than is the molybdenum or GroupVIII component. Higher pH, e.g, up to about 2.5 can also be tolerated inthe more dilute solutions. However, it is still preferable to assurethat the initial pH of even these dilute solutions is within the rangeof 1 to about 2.

Group VIII metals, suitable for use in the invention are iron, cobaltand nickel, ruthenium, rhodium, palladium, osmium, iridium and platinum.The most active Group VIII and Group VI metals are cobalt, nickel,molybdenum and tungsten. The impregnating systems of this invention areparticularly attractive when preparing catalysts of molybdenum and aGroup VIII metal, particularly nickel, due to the relative instabilityof molybdenum containing solutions.

Optimum proportions of the molybdenum and the Group VIII metals in thefinished catalyst will vary over a considerable range, again dependingon the particular metals, the reaction in which the catalyst isemployed, the carrier, etc. Optimum proportionsare best determinedexperimentally and can readily be ascertained by one of ordinary skillin the art. Generally the Group VIII metal, based on the oxide, willcomprise about I to 10, preferably 1 to 6 wt. percent of the catalyst,with the M00 comprising about 5 to 40, preferably 10 to 20 wt. percentof the catalyst.

The required phosphorus-to-Group VI metal oxide in the finished catalystis obtained by employing suitable concentrations of the phosphorus acidand the Group VI metal compound in the impregnating solution. Suitableconcentrations will, of course, vary considerably with the particularGroup VI and Group VIII metal compounds, the phosphorus acid, thecarrier, the pH and temperature of the impregnating solution, method ofeffecting the impregnation, etc., and are best determined empirically.For example, the most preferred acid of phosphorus concentration willnot generally be exactly the same in systems employing different formsof molybdenum or nickel.

Orthophosphoric acid is the preferred source of the phosphorus componentof the catalyst of the invention. However, other phosphorus acids suchas metaphosphoric acid, pyrophosphoric acid, phosphorous acid, etc., maybe used. The compound of the Group VI metal, preferably molybdehum, canbe any one or a combination of a variety of substances which havesufficient solubility in the solution to enable the deposition of thedesired amount of metal. Illustrative compounds are the acids, oxides,and the simple and complex salts such as molybdenum trioxide, molybdenumblue, molybdic acid, ammonium dimolybdate, ammonium phosphomolybdate,ammonium heptamolybdate, nickel and cobalt containing molybdates andphosphomolybdates and the like. Molybdenum is presently preferred sincethe resultant components are the more active conventional components.

The presently preferred Group VIII metal sources are the salts of strongacid anions. Exemplary of such anions are nitrate, sulfate and thehalides, particularly bromide, chloride and fluoride anions. Thispreference is due primarily to the fact that the strong acid anionsdissociate on admixture with the acid of phosphorus and the molybdenumsource to form the corresponding acid. The strong acids are necessary toreduce the pH to a point within the essential range, i.e., l to about 2,at the preferred concentration levels of the respective metal sources.The nitrates are presently the preferred source of the Group VIII metal,nickel nitrate being particularly preferred due to the high activity ofthe resultant catalyst. Ammonium heptamolybdate is the presentlypreferred molybdenum source due to its high solubility. The anions otherthan nitrates are generally less preferred due to significantdifficulties associated with their use. For example, the halides,derived from the Group VIII metal halide source, are useful in preparingthese compositions but result in the evolution of the acidic halide orhydrogen halide gas upon drying and/or calcination. These materials arehighly corrosive and are preferably avoided. The sulfate, on the otherhand, is somewhat more difl'icult to keep in the original solution,making it advisable to employ slightly elevated temperatures, i.e., fromIF to about 150F, depending on the concentrations of the Group VIIImetal sulfate. However, the use of the sulfate salt does have a distinctadvantage. In the preparation of sulfided catalyst the conditions ofcalcination can be controlled so that the sulfate is not completelydriven off and can be chemically reduced to produce a sulfided compositehaving a much more homogeneous distribution of sulfur than couldotherwise be achieved. For example, the sulfate reduction can beconveniently carried out by exposing the calcined catalyst to a reducingatmosphere of hydrogen, carbon monoxide, etc.

A portion of the Group VIII metals can also be added in the form ofsalts of weak acids or as the hydroxides when it is desirable to raisethe pH of the impregnation solution by this procedure. For example, ifthe admixture of the desired amounts of the active metal salts and acidof phosphorus results in a formation of a solution having a pH somewhatlower than desired in a particular application, the pH can be raised bythe addition of a Group VIII metal base such as nickel or cobalthydroxides and carbonates. However, this procedure is not presentlypreferred in that it requires the commensurate correlation of pH andactive metal concentrations. As a result it is presently more preferredto raise the pH when it is initially lower than desired by the additionof a base not having a metal cation, such as ammonia. In any event,where base addition is employed to modify the initial pH, the amount ofadded base should not be so great as to increase the pH to a valueoutside the prescribed range.

Several procedural steps can be employed in the impregnation of thecatalyst substrate with the compositions referred to. One such method,entitled the spray technique, involves spraying the support with asolution of the desired composition. The single-dip or pore volumemethod involves dipping the support in the solution for a periodsufficient to fill the pores with impregnating medium. The applicationof vacuum is generally preferred in the latter approach. Theimpregnating solution can more readily displace air trapped in theinterior pore volume of the catalyst support at reduced pressures.

The amount of active components retained on the support will dependlargely on the pore volume and adsorption capability of the support.Consequently, the characteristics of the support must be taken intoaccount in determining the conditions necessary to obtain a composite ofpredetermined composition. In general, the preferred supports, e.g.,alumina and silica stabilized alumina, will have pore volumes of 0.6 toabout 1.4 cc/gram and adsorption capacity sufficient to retain thedesired amount of solution in a single step. Pore size should also betaken into account in designing the most appropriate systems for theimpregnation of a given support. As a general rule more care should betaken in the preparation of relatively large pore size catalysts. Betterdeposit homogeneity and higher activity are obtained by using longeraging times prior to drying and more gradual drying procedures. Theseobservations are particularly applicable to the impregnation of acidleached supports in which a portion of the pores are usually fairlylarge.

Following either of these procedures the impregnated support can bedried and calcined to produce a catalyst having the desired active metalconcentrations,

provided the concentration of the active metals in the solution issufficient to deposite the desired amount of active metal compound onthe support in a single step. This is one significant advantage of thesenovel solutions. The stability of solutions of much higher activecomponent concentration can be maintained for considerable periods evenin the presence of inorganic supports. When a single step approach isemployed it is, of course, necessary to incorporate a definite amount ofeach active constituent into the impregnating medium and maintain theproper ratios between the several constituents per unit volume ofsolutionin order to obtain a finished catalyst of the desiredcomposition. It is also preferable to age the impregnated particles forat least about 30 minutes and preferably up to about 8 hours beforedrying and calcining. Aging after pore saturation, in the absence ofexcess solution, under mild conditions i.e., F, to about 150F, resultsin more even distribution of active components and improved activity.

Additional precaution should be taken when a support material containingaluminum ions is exposed to excess solution at relatively low pH. It isbelieved that certain constituents of the impregnating solution,particularly the acid of phosphorus, react with aluminum and degrade thesupport, foul the impregnating solution and result in the formation ofundesirable chemical forms on the finished catalyst. As a result, theduration of contacting, particularly with alumina containing supports,is preferably limited to less than about 6 minutes.

Another impregnating method which has found wide application due to theprevious necessity for maintaining relatively low active componentconcentrations is the cyclic or multi-dip procedure wherein the activesupport is repeatedly contacted with impregnating solution with orwithout intermittent drying. As previously mentioned, this procedure isless desirable in that it necessitates the use of procedures far morecompli cated than the single-dip or spray technique. Yetanotherprocedure employed by the prior art, which is not necessary withthese impregnating solutions involves a prolonged contacting step atslightly elevated temperatures, e.g., to F, to promote the incorporationof active components onto the support.

In the circulation dip impregnation procedure the impregnating solutionmay be circulated through a bed or catalyst support particles until therequired amount of the active constituents are deposited. A more dilutesolution having a higher equivalent P/MoO ratio and somewhat higher pHmay be employed when using this technique and the active componentconcentration in the circulating solution can be replenished asnecessary during the impregnation cycle in order to build up the desiredconcentration of active components on the support. Equivalent P/MoO,ratios as low as 0.5 and pH as high as 2.5 may be employed in thisprocess, provided the total concentration of active constituents isreduced by a factor of at least 40% so that the equivalent Group VI andGroup VIII oxide concentrations do not exceed about 17 to about 10,preferably about 14 and 4 wt.%, respectively. These reducedconcentrations are necessitated by the greatly reduced stability of theimpregnating solution due to the higher pH and lower P/MoO, ratios.Nevertheless, the relative ratio of the Group VIII component to theGroup VI component will generally be higher in these dilute systems whenan excess of impregnating medium is employed. This is particularly truein the case of molybdenum, tungsten, nickel and cobalt. It has beenobserved that the Group Vl component combines with the substrate morerapidly than does the Group VIII component. Consequently when depositionof the active components onto the substrate is effected at least in partby adsorption as in the single dip and circulation dip techniques theGroup VIII to Group VI component ratio required to obtain a given finalcomposition is higher than that required in the absence of selectiveadsorption effects. In contrast, the final Group VIII to Group VIcomponent ratio is determined directly by solution composition when thepore saturation of spray techniques are employed. Selective adsorptioneffects are not determinative in these systems.

The exact concentration of the various constituents in the solution mustbe detennined with regard to the final catalyst composition desired, thepore volume of the support particles and the time of contact of thesupport particles and the stability of the impregnating solution. A widerange of active component concentrations can be employed although somelimitations are imposed by the selected impregnation procedure. Forexample, the solutions employed in the spray impregnation or poresaturation technique are usually relatively concentrated. Activecomponent concentrations in these systems should be equivalent to about17 to about 30 weight-percent M and 2 to about 8 weightpercent of theGroup VIII metal oxide, and must be determined in relation to thedesired composition of the final product.

The pH of the solution will generally vary somewhat upon the addition ofthe Group VIII metal salt. The degree of such variation dependsprimarily upon the strength of the salt anion. For example, the additionof nickelous nitrate reduces the pH of the solution somewhat. The degreeof this pH reduction is greater than that experienced when sulfate saltsare employed due to the fact that the nitrate is the anion of a strongeracid than sulfuric acid. As a consequence of this effect, it isgenerally desirable to further adjust the final pH of the solution afteraddition of the Group Vll] metal salt to the preferred value of from Ito about 2, preferably from about 1.3 to about 1.7. If the pH of thefinal solution is lower than about 1 and higher than about 2, thestability of the final solution is reduced with the consequentappearance of precipitates or crystallites.

The desired stability of the impregnating solution is easilydemonstrated by spreading a thin layer of the solution on a glass slideand allowing it to dry gradually under ambient conditions. The stablesolutions prepared by the procedure herein described will dry to acompletely amorphous transparent film as demonstrated by X-raydiffraction examination of the resultant film. Solutions not meetingthese criteria do not form transparent thin films under conditions ofthis test but become opaque or translucent on drying due toprecipitation and/or crystallization.

As illustrated by the examples hereinafter discussed, the catalystsprepared from the less stable impregnating solutions are far less activethan those prepared from the solutions herein described. It appears thatthese differences in activity are attributable, at least in part, to theformation of crystallites and precipitates during impregnation. It isbelieved that this precipitation and crystallite formation results inthe segregation of the several constituents into different crystallinespecies and the consequentformation of heterogeneous active componentdeposits. This type of segregation is prevented by the use'of theimpregnation solutions of this invention.

The catalysts of this invention can be employed in any of the severalhydrocarbon conversion systemslfor which catalytic composites of GroupV! and VIII metals are known to be efi'ective, such as hydrogenation,dehydrogenation, desulfurization, oxidation, denitogenation,demetallization, isomerization, cracking, hydrocracking, and the like.Hydrocarbon feeds employed in such systems include every form andmolecular weight of hydrocarbon compound. However, these catalysts aremost commonly used to convert hydrocarbons boiling from about 200F toabout l,00OF. Hydrogen is generally present in the systems involvinghydrofining, cracking, demetallization and the like, at partialpressures usually in excess of 50 psi, generally 100 to 3,000 psi.Conversion temperatures also vary considerably with the type of feed andthe conversion desired. Most often conversion takes place attemperatures above 600F, usually between 650 and 800F. The preferredcatalysts prepared by single-dip pore saturation with the highly stablerelatively concentrated solutions exhibit such increased hydrofiningactivity that they can be economically employed for deni trogenating anddesulfurizing feeds boiling up to about 1,000F. Such heavy feeds couldnot be feasibly treated with catalysts previously available. Temperatuesinvolved in hydrofining such high end point stocks are usually about700F to about 800F. Hydrogen partial pressures of 750 to 2,000 psi aregenerally employed. The following examples serve to more particularlyillustrate the invention and the advantages thereof.

EXAMPLES l-7 The cstalysts of these examples were all prepared byidentical procedures, with the only variables being the proportions ofthe ingredients, the corresponding impregnation medium, pH and thecarrier. Silicastabilized alumina containing 4.95 percent silica wasemployed in Examples l-3. Alumina stabilized with 6.63 percent silicawas used in Examples 4-7. The catalysts were prepared by a single-dipprocedure inwhich the carrier, in the form of l 16 inch pellets, wasimmeresed in an aqueous impregnation solution containing ammoniumheptamolybdate, nickelous nitrate hexahydrate and orthophosphoric acid,and having the equivalent oxide concentrations reported in Table l. Theparticles were contacted for the designated period under 22 mm. Hg.vacuum and decanted on a No. 5 buchner funnel. The catalysts were thendried and activated by heating at a rate of 50F/hr up to 900F at whichthey were maintained for 2 hours. Each of the catalysts was activated bythe preferred calcination procedure by intimately contacting theimpregnated pellets with 6 to 8 SCF of ambient air at about F inlettemperature per pound of catalyst per minute throughout the period ofdrying and calcination.

The calcination was carried out in a muffle furnace fitted with a finescreen rack on which the specimen was spread in a thin layer, no deeperthan about one half inch, through which air was passed during drying andcalcining. About 500 to 1000 grams of wet impregnated catalyst particleswere placed on a stainless steel screen, 15 X 15 feet square having lessthan 10 mesh per inch. This screen is supported on a perforatedstainless steel tray positioned on a furnace rack in an electricallyheated vertical draft oven having an air inlet at the base. Air wasblown into the bottom of the furnace at a rate of 4 to 12 standard cubicfeet per minute and passed up through the furnace and through the bed ofcatalyst supported on the porous screen.

The hydrofining activity of each catalyst was determined by passing amixed gas oil over a fixed bed of catalyst at a temperature of 725F, apressure of 1,400 psig, space velocity of 2.0 LHSV and a hydrogen rateof 6,000 SCF/barrel of feed. The mixed gas oil feed had a boiling pointrange of 400 to 900F, an API gravity of 23.2 and contained 1.19 weightpercent sulfur and 0.195 weight percent nitrogen. The residual basicnitrogen in the liquid product, after scrubbing with percent sodiumhydroxide, was monitored and used to calculate percent activity withreference to a standard catalyst by the following equation:

(B Feed/B Product (from ,X Cat. -I Log (8,,

Feed/B Product (from Ref. Cat.)) X 100 %Activity Percent denitrogenationwas also calculated from the total nitrogen in the product averaged overthe last 12 hours on the feed. Results are given in Table l in which thedenitrogenation (DeN) activities are expressed as volume percent andweight percent relative to the activity of the reference catalyst. Thelatter is a commercial hydrotreating catalyst consisting of 16.4% M002.9% NiO, and 1.3% P on gamma alumina stabilized with 4.5 weight percentsilica. This catalyst was prepared by impregnating the support with anaqueous system containing 17.4 wt.% M00;, as ammonium heptamolybdate and3.5 wt.% MD as nickel nitrate with a P/MoO weight ratio of 0.085 at a pHgreater than 2.6.

catalyst of Example 1 was the most active even though it contained lessactive metal. The catalyst of Example 3 prepared at an initial solutionpH of 1.3 and a P/MoO; solution ratio of 0.136 exhibited even higheractivity. Example 4, similar to Example 1 in MoO content, P/MoO, ratioand solution pH but employing a different carrier, had an activitysimilar to Example 1. Example 5, in which the equivalent NiO content wassomewhat lower and the initial solution pH was 1.3 had lower activitythan Example 4, but was still considerably more active than the lowPlMoO ratio catalyst of Example 2. Examples 6 and 7 impregnated at pH of1.9 and 1.3 respectively, show that a further increase in the P/MoO,ratios to 0.175 and 0.21, respectively, does not result in any furtherincrease in activity. In fact, the activities of these examples was lessthan that of Examples 3 and 4. The markedly higher activity of thecatalysts prepared from impregnating solutions having pH values, P/MoO,ratios and active component concentrations within the prescribed limitsis readily apparent by comparison with the reference catalyst producedunder conditions preferred by the prior art.

EXAMPLES 8-21 These investigations were conducted to evaluate the effectof impregnating solution composition on the stability of the amorphousdeposits formed in accordance with the method of this invention. Each ofthese solutions was prepared by dissolving ammonium heptamolybdate andphosphoric acid (85 percent) in water 'lAliLE L-COMPOSIIIONS ANDDENIIROGENA'llON ACTIVlIIES OF CATALYSTS O1 EXAMPLES ltcfercncn 16x. 1 11x.2 Ex. 3 Ex. 4 Ex. 5 15x. 11 Ex. 7 catalyst Solution composition,weight percent:

l7. 8 25. 4 20. 4 20. 4 20. 4 17. 8 11!. 8 17, 4 4.0 3.7 3.7 3.7 3.0 4.13.5 2.3 2.3 2.8 2.8 2.50 3.5 1.5 0. 091 0. 136 0. 136 0. 136 0. 140 0.176 0. 085 2.0 1.3 1.3 1.3 1.9 1.3 2.6 Contact time, minutes 15 15 15 1515 120 15 Catalyst composition, weight percent:

15. 2 21. 7 18. 4 18.2 19. 5 18. 4 16. 9 16. 3 2. 95 3. 07 2. 97 2:96 2.88 2. 93 2. 82 2. 8 2.81 2. 2. 96 3. 04 3. 41 3. 26 3. 58 1. 30 0.1850.110 0.162 0.166 0.175 0.175 0.210 O. 080 Activity weight of catalyst,grams 164 175 171 171 175 151 167 146 Volume of DeN activity 140 123 150154 137 140 143 100 Weight percent of DeN activity 125 103 128 132 116127 125 100 Percent DeN 95. 41 94. 00 96. 87 96. 21 96. 56 96. 67 91. S

The volume percent activity of the catalyst of Example 1, in which theP/MoO ratio was 0.185 and the initial pH of the impregnating solutionwas 1.9, was 140 percent of the reference catalyst. The catalyst ofExample 2, in which the P/MoO, weight ratio in the product was only 0.11and the initial pH of the impregnating medium was 2.0, had an activityof only 123 volume percent of the reference catalyst. On a weightpercent basis the difference was even more pronounced on a weight basisof conversion, i.e., 123 versus 103. The for both of these tests arereported in Table 2.

in the proportions reported in Table 2. The indicated amount ofnickelous nitrate hexahydrate was then added to the solution. in severalinstances the pH of the final solution was adjusted upwardly by theaddition of ammonium hydroxide in amounts sufficient to produce theindicated pH change. Each solution was aged overnight (12 hours) at F inglass bottles. Equal portions of each fresh solution were also depositedon glass slides and dried gradually at 75F. Visual observations TABLE 2Example N 8 11 12 13 1-1 16 17 15 11' '30 :l

Ammonium heptamolybdute, g: -11. 0 41. 0 -11. 0 41. 0 11. 0 41. 0 -11. 0-11. 0 -11. 0 -1l. 0 41. 0 41. 0 25. 5 11.0 00 g 33. ti 33. 6 33. 6 33.6 33. ti 33.6 33. 6 33. o 33. ti 33. 6 33.11 33. (l 20.01 t. Phosphoricacid (85%), i: 7. 0 10. -1 12.0 17.0 17. 5 22.0 22.0 27.0 27. 0 17. 022. 0 27. 0 (Ln None 1 1. BS 2. 80 3. 23 4. 57 -1. 70 5.1 1 5.1 1 7. 267. 2G 1. 57 5. 1'1 7. 2o 1. 77 75 75 75 75 75 75 75 75 75 75 75 75 75 T54.5 3.5 2.1 1.7 1.75 1.11 1.5 1.4 1.45 1.75 1.45 1.20 3.7 5-6. 0 24. 021. 0 21. 0 24. 0 21. 0 21. 0 24. 0 24. 0 2-1. 0 24.0 2-1. 0 2-1. 0 16.5 2-1. 0 NiO, t: 6.16 6.16 6.10 6.16 6.10 0.10 13.16 6. 16 0.10 6.166.16 6.16 -1. 24 6.1:. Total volume 01 solution, m1 120 120 120 120 120120 120 120 120 110 110 100 120 120 [)II 3.5 2.3 1.11 1.3 1.25 1.15 1.11.05 1.0 1.3 1.0 0.0 2.6 4 Adjust pH with llNiOll None None None None 1.60 \one 1. 60 None 1. T0 2. 3 2. 3 2. 3 None \on Final volume, 1111 120120 120 120 123. 5 120 125 132 120 121 118 120 l; M00 [5 /cc 0. 2825 0.2825 0.2825 0. 2825 0. 280 0. 2825 0.268 0.2825 0.255 0. 2825 0.2825 0.2825 0. 1742 0. 2825 N10, i:./cc.- 0.0517 0.0517 0.0517 0.0517 0.05150.0517 0.0512 0.0517 0.057 0. 0517 0.0517 0. 0511 0.0353 0.0517 1',p;./cc 0.0157 0.0233 0. 0261! 0. 0381 0. 0380 0. 011 3 0. 0172 0. 06050. 055 0. 0380 0. 0172 0.0705 0. 0148 4 P/MOO3 weight rat v 0. 056 0.083O. 0115 0. 136 0. 136 0. 176 0. 176 0.216 0. 21ti 0. 136 0. 176 0.216 0.085 000 Dried film on glass slide... Yellowish opaque TransparentI-nmcracking t?) Solution characteristics after 12 hours. 0) l '1 1Slightly opaque.

2 Transparent.

1 Opaque yellow.

4 Crystalline deposit. Yellow fine crystalline precipitate. 6 Clear.

'- lraee sediment.

7 Glass bottles containing the 3 solutions were lined with crystallinematerial. p11 is too high for stable solution.

1 Prev. w/yellow lines formed slowly. v \Vhittprecipitate begins to formin 5 10 Hill]. olunnnous after 1 ln'.

The impregnating solutions of Examples 8, 9 and 10 were all unstable asindicated by the formation of yel lowish opaque precipitates on theglass slides and the formation of yellow fine crystalline deposits inthe solutions aged for 12 hours at 75F. The observed instability isbelieved to be attributable to the low solution P/MoO weight ratios, allof which are below the minimum of about 0.10 necessary to obtain theadvantages of this invention. It is interesting to note, however, thatthese ratios are equivalent to those considered preferable by the priorart. In addition, the solutions of Examples 8 and 9 have pH values of3.5 and 2.3, respectively, both of which exceed the maximum-pH of 2.0tolerable in these relatively concentrated solutions. The precipitateformation observed in Example 10 at a pH of 1.9 and P/MoO, weight ratioof 0.095 was much slower than that observed in either Examples 8 or 9,although the dried film definitely exhibited an opaquenesscharacteristic of a heterogeneous or cyrstalline system. The presence ofprecipitate in the aged solution was apparent after 12 hours. Althoughthe degree of instability was reduced by reducing the pH to 1.9 inExample 10, the P/MoO weight ratio was so far below the necessaryminimum of about 0.1 that some instability was apparent in the driedfilm and aged solution.

Examples 11 through 14 were conducted at conditions of pH and P/MoO,ratio within the limits prescribed by this discovery and illustratedremarkable stability in both the dried films and aged solutions. A traceamount of precipitate was observed in the solution of Example 12 after12 hours of aging at 75F. However there was no concurrent opaqueness inthe dried film and the aged solution was evidently far more stable thanthe solutions of Examples 8-10. The presence of the trace precipitate inthe aged solution of Example 12 is attributed to the addition ofsufficient ammonium hydroxide to increase the pH from the original valueof 1.25 to the final value of 1.60. It isbelieved that the presence ofammonium hydroxide in solutions having P/MoO, ratios approaching thelower prescribed limit of about 0.1, i.e., 0.136 in Example 12, tends toreduce the stability of those solutions. This conclusion is born out byExample 14 in which sufficient ammonium hydroxide was added to thesolution to increase the pH from the original value of 1.1 to a final pHof 1.60. The P/MoO ratio in that preparation was 0.176 which was highenough to counteract the effect of base addition as indicated by thecomplete absence of any opaqueness or precipitate in either the .driedfilm or aged solution.

sediment were present in the aged solution. Although solutions of thisnature are less preferred, they are still far superior to the solutionsenvisioned by the prior art and illustrated by Example 20. Thatsolution, having a pH of 2.6 and a P/MoO, ratio of 0.085 produced anopaque yellow heterogeneous deposit on the glass slide. The formation offine yellow particulate matter was evident in the aqueous solutionthroughout the aging period. The significance of the poor stability ofthat solution is even more apparent when it is observed that the totalmetals concentration in Example 20 was about 85 percent less than thestable solution of this invention.

' Obviously the tendency toward precipitation is greater at higherconcentrations. Yet the solution of this invention remained stable atconcentrations about percent higher than that at which substantialinstability was observed in Example 20.

It should also be observed that the value of this dis tinction becomeseven more apparent in the context of catalyst preparation systems. Thesavings in time and investment alone afforded by single-stepimpregnation techniques is perspicuous. Yet the application of suchtechniques requires the use of impregnating solutions of relatively highconcentrations to enable the deposition of the desired amounts of activecomponents. The markedly superior compositions of this invention enablethe use of those systems to produce catalysts of superior activity.

' The composition of Example 16 having a P/MoO weight ratio identical toExample 15 and an initial pH of 1.0 was further treated by the additionof sufi'lcient ammonium hydroxide to increase the pH to 1.70. Theresultant solution was very stable and produced a completely transparentdried film. The aqueous solution remained completely clear even afteraging for 12 hours.

The effect of higher pH on the stability of impregnating solutionshaving active component concentrations sufficient to enable the use ofsingle-step impregnating methods is illustrated by Examples l7l9.Several P/MoO ratios were investigated in these examples. All three ofthese solutions having pH values of 2.3 and P/MoO, ratios representativeof the prescribed range were much less stable than the solutions ofExamples 1 1-16. The formation of opaque cracked films and substantialcrystallization in the aged solutions were observed in each instance.

The solution of Example 21 provides a contrast between the stablesolutions having pH values and P/MoO, ratios within the necessary limitsto similar prior art solutions prepared at higher pH in the absence ofan acid or phosphorus.

EXAMPLES 22 and 23 These two examples illustrate the influence of agingthe substrate in contact with impregnating medium on the activity of theresultant catalyst.

A solution containing 410 grams of ammonium heptamolybdate, 210 grams of85 percent orthophosphoric acid and 220 grams of nickelous nitratehexahydrate made up to a total volume of 950 ml, and pH adjusted to 1.3by the addition of several ml of concentrated ammonium hydroxide wasdripped from a separatory funnel onto 1,300 grams of silica-stabilizedalumina extrudates in an evacuated 4liter flask. The flask wasvigorously shaken by hand during and after the addition of the solutionto aid in its distribution. This volume of solution was enough to fillthe pore volume of the extrudates and wet them enough so that theyadhered to each other and the flask. There was no free liquid in theflask. The agitation under vacuum was continued for minutes. Thetemperature of the wet extrudates increased from about 77F to about 122Fduring this period of time. The wetted and impregnated extrudates weredivided into two parts.

A 1,000 gram portion of the impregnated extrudates which had been agedfor 20 minutes was spread on a stainless steel screen tray in the Kressbox muffle furnace and dried at 200F for 16 hours. The dried pelletswere then distributed on a stainless steel screen suspended within atop-opening Kress muffle furnace and heated at a controlled rate of 50Fper hour to 900F, at which temperature they were maintained for 2additional hours. Throughout the entire drying and calcina tion periodambient air, having an inlet temperature of 75F was passed into thebottom of the furnace and over the pellets at a rate of about 7 standardcubic feet per minute per pound of catalyst.

The remaining material in the 4-liter impregnating flask was aged underambient conditions with occasional shaking by hand for an additional 100minutes. The impregnated and aged extrudates were then distributed on a15 inches square stainless steel tray and placed in an oven at ambientconditions. The oven was turned on and heated to 200F and the catalystwas held held at that temperature for 16 hours. House vacuum was appliedto draw air through the oven during this period. The dried extrudateswere then calcined in the Kress box-type muffle as described above. Thecomposition and activity of these two catalysts were determined as inExample 3 and are compared in Table 3.

These results demonstrate that considerable advantage can be achieved byaging catalysts impregnated by single step pore saturation.

1 claim:

1. As a stable impregnating medium an aqueous solution which fonns onadmixing at least one water soluble molybdenum compound, at least onewater soluble compound of nickel or cobalt and an acid of phosphoruswith water in proportions equivalent to 10 to about 30 wt.% M00 about 1to about 10 wt. percent nickel or cobalt oxide, and a P/MoO, weightratio of 0.1 to 0.25, said solution having a pH below about 2.

2. The composition of claim 1 wherein said solution contains at leastone water soluble basic material selected from ammonia, ammoniumhydroxide, and the hydroxides and carbonates of nickel and cobalt.

3. The composition of claim 1 having an equivalent M00, concentration ofabout 17 to about 30 wt. percent and an equivalent nickel or cobaltoxide concentration of about 1 to about 8 wt. percent.

4. The composition of claim 1 wherein said acid of phosphorus isorthophosphoric acid, and said molybdenum compound is selected frommolybdic acid, molybdenum trioxide, ammonium heptamolybdate, ammoniumphosphomolybdate and molybdenum blue.

5. The composition of claim 4 wherein said compound of nickel or cobaltis selected from the nitrates, sulfates, hydroxides, carbonates,fluorides, chlorides and bromides of nickel and cobalt.

6. The composition of claim 5 wherein said P/MoO ratio is from about0.12 to 0.23 and the pH of said solution is within the range of about1.2 to about 1.8.

7. The stable aqueous solution which fonns on admixing at least onemolybdenum source selected from ammonium heptamolybdate, ammoniumphosphomolybdate, molybdic acid, molybdenum trioxide and molybdenumblue, a water soluble Group VIII metal compound of nickel or cobalt, andorthophosphoric acid with water in amounts corresponding to 17 to about30wt.% M00,, 2 to about 10 wt. percent of the corresponding Group Vlllmetal oxide, and a P/MoO, weight ratio of about 0.1 to about 0.25, saidsolution having a pH of about 1 to about 2.

8. A method of producing a catalyst including the steps of impregnatinga foraminous carrier with an aqueous solution which forms on admixing atleast one water soluble molybdenum compound, at least one water solublethermally oxidizable Group Vlll metal compound of nickel or cobalt andan acid of phosphorus in water in proportions equivalent to 10 to about30 wt.% M00,, about 1 to about 10 wt. percentof the corresponding GroupVIII metal oxide, and a P/MoO, weight ratio of 0.1 to about 0.25, the pHof said solution being below about 2, and thennally activating the thusimpregnated carrier.

9. The method of claim 8 wherein said Group Vlll metal is selected fromnickel and cobalt and said acid of phosphorus is selected fromorthophosphoric, r'netaphosphoric, pyrophosphoric and phosphorous acids.

10. The method of claim 8 wherein said Group VIII metal compound isselected from the nitrates, sulfates, hydroxides, carbonates, fluorides,chlorides and bromides of nickel and cobalt and said molybdenum compoundis selected from ammonium heptamolybdate, ammonium phosphomolybdate,molybdic acid, molybdenum trioxide and molybdenum blue.

11. The method of claim 8 wherein said molybdenum compound is ammoniumheptamolybdate, said Group VIII compound is selected from the nitrateshydroxides, carbonates, sulfates, fluorides, chlorides and bromides ofnickel and cobalt, said acid of phosphorus is orthophosphoric acid andsaid carrier comprises one of silica and alumina.

12. A method of producing a catalyst including the steps of impregnatinga foraminous carrier with the solution which forms on admixing at leastone molybdenum source selected from ammonium heptamolybdate, ammoniumphosphomolybdate, molybdic acid, molybdenum trioxide and molybdenumblue, a water soluble Group VIII metal compound of cobalt or nickel andorthophosphoric acid with water in amounts corresponding to about 17 toabout 30 wt.% M about I to about I0 wt. percent of the correspondingGroup VIII metal oxide, and a P/MoO, weight ratio of 0.1 to about 0.25,wherein the pH of said solution is below about 2.

13. The catalytic composition prepared by the method including the stepsof impregnating a foraminous support with the aqueous inpregnatingmedium which fonns an admixture of at least one molybdenum compoundselected from ammonium heptamolybdate, molybdic acid, molybdenumtrioxide and molybdenum blue, at least one water soluble Group VIIImetal compound selected from the sulfates, nitrates, fluorides,chlorides, bromides, carbonates and hydroxides of cobalt and nickel andan acid of phosphorus with water in proportions equivalent to about l0to about 30 weight-percent MoO about I to about wt. percent of thecorresponding Group VIII metal oxide, and a P/MoO weight ratio of about0.I to about 0.25, and calcining the resulting composite in an oxidizingatmosphere, wherein the pH of said solution is below about 2.

14. The composition of claim 13 wherein said Group I VIII metal compoundis present in said impregnating medium in an amount corresponding toabout 2 to about 8 weight percent of the corresponding metal oxide, saidmolybdenum compound is ammonium heptamolybdate, said acid of phosphorusis orthophosphoric acid and the concentration of said molybdenumcompound corresponds to about 17 to about 24 wt.% M00 15. The catalyticcomposition of claim 13 having an equivalent M00; content of about 5 toabout 40 wt. percent, an equivalent Group VIII metal oxide content ofabout I to about 10 wt. percent and a P/MoO; ratio of about 0.12 toabout 0.25 and wherein said support contains silica or alumina.

16. The composition of claim 13 wherein said impregnated carrier is agedin contact with said medium prior to drying for at least about 30minutes.

17. The composition of claim 13 having the equivalent oxideconcentration of 10 to 20 wt.% M00 and a P/MoO, ratio of 0.12 to 0.25.

18. The composition prepared by the method including the steps ofimpregnating a foraminous carrier with the solution which forms upon theadmixture of water and ammonium heptamolybdate in amounts equivalent toabout 17 to about 30 wt.% M00 at least one Group VIII compound selectedfrom the nitrates, hydroxides, carbonates, chlorides and sulfates ofnickel and cobalt in total amounts corresponding to about 2 to about 8wt. percent of the corresponding oxides, and orthophosphoric acid in anamount sufficient to provide a P/MoO, ratio of about 0.1 to about 0.25in said solution and calcining the resultant impregnated carrier, the pHof said solution initially contacted with said carrier being below about2.

19. The composition of claim I8 wherein said salt of said Group VIIIcompound is selected from nickel nitrate and cobalt nitrate and saidforaminous support is aged in contact with said solution for at least 30minutes. 4

20. A catalyst prepared by the method including the steps ofimpregnating an alumina containing support with a solution formed on theadmixture of water and at least one molybdenum compound selected fromammonium heptamolybdate, molybdic acid, molybdenum trioxide andmolybdenum blue in amounts suflicient to provide an equivalent M00concentration of about 17 to about 30 wt. percent, at least one GroupVIII compound selected from the nitrates, hydroxides, carbonates,sulfates, fluorides, chlorides and bromides of nickel and cobalt inamounts corresponding to about 2 to about 8 wtdpercent of the equivalentoxide, and orthophosphoric acid in amounts sufficient to provide aP/MoO, weight ratio of from about 0.1 to about 0.25 in said'solution ata temperature and for a period of time sufficient to produce a catalysthaving an equivalent MoO, content of about 5 to about 40 wt. percent, anequivalent nickel and/or cobalt oxide content of from about I to about10 wt. percent, and a P/MoO weight ratio of from about 0.12 to about0.25 and calcining the thus impregnated support, wherein the pH of saidsolution initially contacted with said support is below about 2.

2. The composition of claim 1 wherein said solution contains at leastone water soluble basic material selected from ammonia, ammoniumhydroxide, and the hydroxides and carbonates of nickel and cobalt. 3.The composition of claim 1 having an equivalent MoO3 concentration ofabout 17 to about 30 wt. percent and an equivalent nickel or cobaltoxide concentration of about 1 to about 8 wt. percent.
 4. Thecomposition of claim 1 wherein said acid of phosphorus isorthophosphoric acid, and said molybdenum compound is selected frommolybdic acid, molybdenum trioxide, ammonium heptamolybdate, ammoniumphosphomolybdate and molybdenum blue.
 5. The composition of claim 4wherein said compound of nickel or cobalt is selected from the nitrates,sulfates, hydroxides, carbonates, fluorides, chlorides and bromides ofnickel and cobalt.
 6. The composition of claim 5 wherein said P/MoO3ratio is from about 0.12 to 0.23 and the pH of said solution is withinthe range of about 1.2 to about 1.8.
 7. The stable aqueous solutionwhich forms on admixing at least one molybdenum source selected fromammonium heptamolybdate, ammonium phosphomolybdate, molybdic acid,molybdenum trioxide and molybdenum blue, a water soluble Group VIIImetal compound of nickel or cobalt, and orthophosphoric acid with waterin amounts corresponding to 17 to about 30 wt.% MoO3, 2 to about 10 wt.percent of the corresponding Group VIII metal oxide, and a P/MoO3 weightratio of about 0.1 to about 0.25, said solution having a pH of about 1to about
 2. 8. A method of producing a catalyst including the steps ofimpregnating a foraminous carrier with an aqueous solution which formson admixing at least one water soluble molybdenum compound, at least onewater soluble thermally oxidizable Group VIII metal compound of nickelor cobalt and an acid of phosphorus in water in proportions equivalentto 10 to about 30 wt.% MoO3, about 1 to about 10 wt. percent of thecorresponding Group VIII metal oxide, and a P/MoO3 weight ratio of 0.1to about 0.25, the pH of said solution being below about 2, andthermally activating the thus impregnated carrier.
 9. The method ofclaim 8 wherein said Group VIII metal is selected from nickel and cobaltand said acid of phosphorus is selected from orthophosphoric,metaphosphoric, pyrophosphoric and phosphorous acids.
 10. The method ofclaim 8 wherein said Group VIII metal compound is selected from thenitrates, sulfates, hydroxides, carbonates, fluorides, chlorides andbromides of nickel and cobalt and said molybdenum compound is selectedfrom ammonium heptamolybdate, ammonium phosphomolybdate, molybdic acid,molybdenum trioxide and molybdenum blue.
 11. The method of claim 8wherein said molybdenum compound is ammonium heptamolybdate, said GroupVIII compound is selected from the nitrates hydroxides, carbonates,sulfates, fluorides, chlorides and bromides of nickel and cobalt, saidacid of phosphorus is orthophosphoric acid and said carrier comprisesone of silica and alumina.
 12. A method of producing a catalystincluding the steps of impregnating a foraminous carrier with thesolution which forms on admixing at least one molybdenum source selectedfrom ammonium heptamolybdate, ammonium phosphomolybdate, molybdic acid,molybdenum trioxide and molybdenum blue, a water soluble Group VIIImetal compound of cobalt or nickel and orthophosphoric acid with waterin amounts corresponding to about 17 to about 30 wt.% MoO3, about 1 toabout 10 wt. percent of the corresponding Group VIII metal oxide, and aP/MoO3 weight ratio of 0.1 to about 0.25, wherein the pH of saidsolution is below about
 2. 13. The catalytic composition prepared by themethod including the steps of impregnating a foraminous support with theaqueous inpregnating medium which formS an admixture of at least onemolybdenum compound selected from ammonium heptamolybdate, molybdicacid, molybdenum trioxide and molybdenum blue, at least one watersoluble Group VIII metal compound selected from the sulfates, nitrates,fluorides, chlorides, bromides, carbonates and hydroxides of cobalt andnickel and an acid of phosphorus with water in proportions equivalent toabout 10 to about 30 weight-percent MoO3, about 1 to about 10 wt.percent of the corresponding Group VIII metal oxide, and a P/MoO3 weightratio of about 0.1 to about 0.25, and calcining the resulting compositein an oxidizing atmosphere, wherein the pH of said solution is belowabout
 2. 14. The composition of claim 13 wherein said Group VIII metalcompound is present in said impregnating medium in an amountcorresponding to about 2 to about 8 weight percent of the correspondingmetal oxide, said molybdenum compound is ammonium heptamolybdate, saidacid of phosphorus is orthophosphoric acid and the concentration of saidmolybdenum compound corresponds to about 17 to about 24 wt.% MoO3. 15.The catalytic composition of claim 13 having an equivalent MoO3 contentof about 5 to about 40 wt. percent, an equivalent Group VIII metal oxidecontent of about 1 to about 10 wt. percent and a P/MoO3 ratio of about0.12 to about 0.25 and wherein said support contains silica or alumina.16. The composition of claim 13 wherein said impregnated carrier is agedin contact with said medium prior to drying for at least about 30minutes.
 17. The composition of claim 13 having the equivalent oxideconcentration of 10 to 20 wt.% MoO3 and a P/MoO3 ratio of 0.12 to 0.25.18. The composition prepared by the method including the steps ofimpregnating a foraminous carrier with the solution which forms upon theadmixture of water and ammonium heptamolybdate in amounts equivalent toabout 17 to about 30 wt.% MoO3, at least one Group VIII compoundselected from the nitrates, hydroxides, carbonates, chlorides andsulfates of nickel and cobalt in total amounts corresponding to about 2to about 8 wt. percent of the corresponding oxides, and orthophosphoricacid in an amount sufficient to provide a P/MoO3 ratio of about 0.1 toabout 0.25 in said solution and calcining the resultant impregnatedcarrier, the pH of said solution initially contacted with said carrierbeing below about
 2. 19. The composition of claim 18 wherein said saltof said Group VIII compound is selected from nickel nitrate and cobaltnitrate and said foraminous support is aged in contact with saidsolution for at least 30 minutes.
 20. A catalyst prepared by the methodincluding the steps of impregnating an alumina containing support with asolution formed on the admixture of water and at least one molybdenumcompound selected from ammonium heptamolybdate, molybdic acid,molybdenum trioxide and molybdenum blue in amounts sufficient to providean equivalent MoO3 concentration of about 17 to about 30 wt. percent, atleast one Group VIII compound selected from the nitrates, hydroxides,carbonates, sulfates, fluorides, chlorides and bromides of nickel andcobalt in amounts corresponding to about 2 to about 8 wt. percent of theequivalent oxide, and orthophosphoric acid in amounts sufficient toprovide a P/MoO3 weight ratio of from about 0.1 to about 0.25 in saidsolution at a temperature and for a period of time sufficient to producea catalyst having an equivalent MoO3 content of about 5 to about 40 wt.percent, an equivalent nickel and/or cobalt oxide content of from about1 to about 10 wt. percent, and a P/MoO3 weight ratio of from about 0.12to about 0.25 and calcining the thus impregnated support, wherein the pHof said solution initially contacted with said support is below about 2.